、。
That sort of thing is just different between boys and girls, I'm telling you.
Literal
That-area [topic-は], boys [and-と] girls [at-で][topic-は] differ-[explanatory-んだ]-[I said-ってば].
そこらへん (or そこら辺) is a vague demonstrative 'that area / that kind of thing,' used to refer to an unspecified domain the speakers have been discussing. Xと(Y)とでは is a comparative construction 'between X and Y.' ってば is an emphatic repetition-marker implying 'I've already said this / I'm telling you,' typical of slightly frustrated casual speech. The double topic marking (the outer は on そこらへん and the contrastive では) frames the sentence as reasserting a contrast the speakers have been debating.